Microfabrication using photolithography techniques has conventionally been performed in manufacturing of semiconductor devices. The microfabrication is a process of forming a thin film of a photoresist composition on a substrate to be processed, such as a silicon wafer, radiating active light such as ultraviolet rays thereon through a mask pattern having semiconductor device patterns, developing the pattern, and etching the substrate to be processed, such as a silicon wafer, using the resulting photoresist pattern as a protection film (mask). With the increasing density of semiconductor devices in recent years, the active light used have been changed to those at shorter wavelengths, for example, from a KrF excimer laser (a wavelength of 248 nm) to an ArF excimer laser (a wavelength of 193 nm). Accordingly, the effects of diffuse reflection of active light from the substrate or standing waves become a serious issue, and a method has been widely adopted in which an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) is provided as a resist underlayer film between the photoresist and the substrate to be processed for serving the function of preventing reflection.
Known examples of the anti-reflective coatings include: inorganic anti-reflective coatings including, for example, titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, and α-silicon; and organic anti-reflective coatings made from a light absorbing substance and a polymer compound. The former requires systems for forming films, such as a vacuum deposition apparatus, a CVD apparatus, and a sputtering apparatus, whereas the latter requires no special system. In this respect, organic anti-reflective coatings are advantageous and have been elaborately examined.
An ArF immersion lithography technique in which exposure is performed through water has been in actual use in recent years as a next-generation photolithography technique that replaces the photolithography technique using ArF excimer laser (a wavelength of 193 nm). The photolithography techniques using light, however, have been approaching their limits. An EUV lithography technique using EUV (a wavelength of 13.5 nm) has been attracting attention as a new lithography technique after the ArF immersion lithography technique. In the semiconductor device manufacturing process using EUV lithography, a substrate coated with an EUV resist is exposed by EUV radiation and developed to form a resist pattern.
In order to protect the EUV resist from contaminants or to block undesired radiation such as UV or DUV (out of band (OOB)), a method has been described, in which the overlayer of the EUV resist includes a polymer including a group containing at least one of beryllium, boron, carbon, silicon, zirconium, niobium, and molybdenum (Patent Document 1 and Patent Document 2).
In order to block OOB, for example, onto an overlayer of the EUV resist, a top coating comprising a polyhydroxystyrene (PHS) compound, an acryl compound, or the like is applied to reduce OOB (Non-Patent Document 1), and onto an overlayer of the EUV resist, a film that is called an EUV resolution enhancement layer is applied so that OOB is absorbed to improve the resolution of the EUV resist (Non-Patent Document 2); however, there are no descriptions for what types of compositions are optimal. In addition, a novolac material comprising a naphthalene ring is described as a resist overlayer film forming composition for EUV lithography (Patent Document 3).